join stdin

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static char *build_format(int bufsiz) {
  char *format = calloc(1, bufsiz);
  if (!format) {
    exit(1);
  }
  sprintf(format, "%%%d[^\n]%%*c", bufsiz - 1);
  return format;
}
static char *read_to(char **buf, int bufsiz) {
  char *format = build_format(bufsiz);
  *buf = calloc(1, bufsiz);
  int n = scanf(format, *buf);
  free(format);
  if (n != 1) {
    free(*buf);
    return NULL;
  }
  return *buf;
}
static char *append_to(char **acc, char *s) {
  *acc = realloc(*acc, strlen(*acc) + strlen(s) + 1);
  if (!*acc) {
    exit(1);
  }
  strcat(*acc, s);
  return *acc;
}
int main(void) {
  char *acc = calloc(1, 1);
  *acc = '\0';
  for (char *buf = NULL; read_to(&buf, BUFSIZ); free(buf)) {
    if (*buf == ',') {
      free(buf);
      break;
    }
    append_to(&acc, buf);
  }
  printf("%s\n", acc);
  free(acc);
}